Microfilm reader with microfilm and reticle images provided to each of two binocular eyepieces

ABSTRACT

A process for high resolution high accuracy photoreduction of radiographs, a rotatable photographic copy stand for the photoreduction process, and a high resolution high accuracy microfilm reader with built-in measuring capabilities are shown. The photoreduction process employs a camera with high precision optics, a high resolution copy film, and a first developing solution containing 0.014 to 0.025 moles per liter of a 3-pyrazolidone as the primary developing agent plus a lesser amount of a secondary developing agent, in a reversal process, to yield positive images having gamma values of 1.00 to 1.05. The copy stand has multiple workstations mounted on a rotatable frame, and several lightboxes. The microfilm reader employs high precision optics throughout, and possesses a variable magnification objective lens, a beam splitter, ultrawide-angle eyepieces, and a movable measuring reticle, the image of which is superimposed upon the image from the objective lens for accurate measurement of features shown on a film being examined. By means of the disclosed process and apparatus, industrial radiographs or other sorts of X-rays are photoreduced and later reenlarged for reexamination and measurement of selected features, with an overall dimensional accuracy of at least 99.9%.

This application is a continuation of application Ser. No. 06/888,114,filed July 18, 1986, now abandoned.

FIELD OF THE INVENTION

This invention relates to photoreduction and viewing of X-ray films, andmore particularly to a process and apparatus for high resolution, highaccuracy photoreduction of industrial radiographs and accurate retrievalof the photoreduced images.

BACKGROUND OF THE INVENTION

In a number of high-technology fields, as for example the nuclearindustry, the aerospace industry, the pipeline industry, and themilitary, it is frequently required practice to X-ray criticalcomponents to screen for defects. The resulting radiographs are sheetsof film up to about 14×17 inches. Hundreds of thousands of theseradiographs are taken each year and stored for record-keeping purposes.Such storage is very expensive because of the sheer bulk of materialinvolved, and the correspondingly large amounts of storage spacerequired. Storage of individual radiographs also presents possibleproblems of loss of particular records by theft or misfiling.

Several years ago the Nuclear Regulatory Commission (NRC) revised itsregulations to authorize nuclear power plants to photoreduce theirrecords instead of storing the originals. To date, however, it has notbeen possible to realize the very substantial cost savings suchphotoreductions would represent, because a process and apparatus foraccurately photoreducing these industrial radiographs and recoveringthem undistorted has not been available. The technical specificationsfor photoreduction and recovery of the full information content of suchradiographs are very severe, the NRC regulations and the ASTM standardsrequiring optical distortion to be not more than 0.1%. This is becauseit may be necessary at some later time to measure recorded defects andcompare the result to the regulatory code standards. The above standardof accuracy also satisfies or exceeds the requirements of all otherproducers of radiographs.

Although the requirements for accuracy in the photoreduction andreproduction of industrial radiographs are very high, the standards withrespect to optical densities are not so severe. It is not necessary thatan acceptable photoreduction and reproduction system reproduce opticaldensities of the original film with an extremely high degree ofaccuracy. It is, however, necessary that the relative optical densitiesof different portions of the films be preserved.

The apparatus and procedures employed routinely in the medical field tophotoreduce medical X-rays and reenlarge them for later viewing will notserve for the photoreduction and reenlargement of the industrialradiographs which are the subject of the preset invention, because thedemands for accuracy in the medical field are much less severe than inthe nuclear regulatory field and in other critical industrialapplications. As a result, the photographic processes and apparatusemployed to photoreduce and subsequently reproduce medical X-rays do notmeet the required standards for photoreduction and subsequentreenlargement of industrial radiographs for regulatory purposes.

Accordingly, it would be very desirable to have available a photographicprocess and apparatus capable of photoreducing industrial radiographswith extremely high resolution and accuracy, and reenlarging the reducedradiographs with essentially no loss in resolution or accuracy, whilesimultaneously maintaining the relative optical densities of theoriginal radiographs.

SUMMARY OF THE INVENTION

The above-identified deficiencies of the prior art have been overcomeand the desired photographic process and apparatus for photoreducing andsubsequently reenlarging industrial radiographs with extremely highresolution, dimensional accuracy, and reproducibility of relativeoptical densities are provided by the present invention.

In accordance with the invention, industrial radiographs arephotoreduced with high resolution and accuracy, and with preservation ofrelative optical densities of the original film, by application of aprocess having the following steps: illuminating a radiograph uniformlyfrom the rear; providing a camera having optics that produce no morethan 0.1% total distortion in any dimension; determining proper exposureby measuring light transmitted by the light areas and the dark areas ofthe subject radiograph and combining these light readings appropriately;photographing the radiograph on a high resolution thin emulsion lightsensitive silver halide film employing the proper exposure derived forthe particular radiograph; and developing the exposed film in a reversalprocess to a positive image having a gamma value in the range of about1.00 to about 1.05, the reversal process further including the steps oftreating the film with an aqueous first developer solution having aconcentration of about 0.014 moles per liter to about 0.025 moles perliter of a 3-pyrazolidone as primary developing agent and including atleast one secondary developing agent at a concentration in the firstdeveloper solution less than the concentration of the 3-pyrazolidone.Following the first development, the negative is chemically bleached,reexposed, redeveloped with an active developer, treated with a fixingsolution, washed, and dried. If desired, several radiographs of a singleworkpiece may be accurately superimposed and photographed together toform a composite photoreduced image having essentially all of theinformation contained in the several original radiographs separately.

The photocopying operation is conveniently carried out on an industrialscale by the use of a photographic copy stand having a base, a pedestalmounted on the base, at least one lightbox mounted approximatelyhorizontally on the pedestal, a unitary frame which is attached to thepedestal above the lightboxes in a manner permitting rotation of theframe about the pedestal, a plurality of workstations mounted on theunitary frame, with each of the workstations including a clear flatglass plate and a mechanism for holding an industrial radiographic filmon the glass, and at least one camera-supporting arm mounted on thepedestal, each arm being shaped and disposed to hold a camera directlyover one of the lightboxes. Multiple original photoreduced positives arethus readily made, providing records for both archival storage and forready access. Details of operation of the copy stand are presented inthe detailed description, below.

The films produced in the photoreduction process discussed above are"blown back" accurately to full scale for reexamination andremeasurement of any features, using a high resolution microfilm readerhaving a supporting chassis, a focusing mount attached to the chassis ina manner such that it can be positionally adjusted relative to thechassis, a binocular microscope head attached to the focusing mount andincluding eyepiece tubes and ultrawide-angle eyepieces, a beam splitterassembly attached to the focusing mount and including a beam splitterand a housing for holding the beam splitter, a variable magnificationobjective lens attached to the beam splitter housing, and a measuringreticle assembly attached to the beam splitter housing, this reticleassembly containing a reticle and means for projecting an image of thereticle into the beam splitter. The optical system taken as a wholeproduces no more than 0.1% total distortion when the reader is properlyadjusted and operated. The operation of the microfilm reader isdiscussed in the detailed description, below.

DESCRIPTION OF THE DRAWING

The invention will be better understood from a consideration of thedetailed description taken in conjunction with the drawing in which:

FIG. 1 is a flow chart illustrating the steps of the photoreductionprocess;

FIG. 1a is a schematic of the exposure-calculating andcamera-controlling circuitry;

FIG. 2 is a perspective view of the copy stand of the invention;

FIG. 3 is a side view of the copy stand;

FIG. 4 is a top view of the copy stand;

FIG. 5 is a perspective view of the high resolution microfilm reader ofthe invention; and

FIG. 5a is a schematic of the reticle assembly.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, there is shown a schematic flow chartillustrating the steps of a process for photoreducing industrialradiographs with high resolution and accuracy, while maintainingaccurate relative optical densities of the original radiograph beingphotographed. The subject radiograph is first illuminated uniformly fromthe rear in step 10. This illuminating step is preferably accomplishedby means of a lightbox having a lighted surface and a light output whichvaries by less than 10% over the lighted surface. A camera having opticsproducing no more than 0.1% total distortion in any dimension isprovided in step 12 and a proper exposure is determined in step 14 bymeasuring the light transmitted by both the light and dark areas of theradiograph and combining these readings appropriately.

A high quality 35 mm camera is preferably employed in this process. Thecamera lens should produce no more than 0.1% distortion in anydimension, and should vary less than one-third stop from center to edgein its light transmitting properties. Suitable commercial lenses meetingthese criteria are the 55 mm Micro Nikkor and the 50 mm Olympus MicroZuiko.

Commercial camera lenses may typically vary in their focal lengths by asmuch as 5% from the nominal focal length. This is not a critical factor,however, since compensating adjustments are made in the camera mountduring set-up. To ensure the accuracy of measurements taken from thereduced image, a scale having the same graduations as the reticle imageof the microfilm reader discussed below and positioned at the same planeas the original material is photographed with the radiograph. Aligningthe photographed scale with the reticle image and adjusting themagnification of the reader to match guarantees accuracy.

The determination of proper exposure in step 14 is made with a lightsensing probe which is preferably deployed close to the area of theradiograph being measured, for highest accuracy in the determination ofthe light transmitted by the dark and light portions of the radiograph.The light sensing probe is connected to electronic circuitry whichcalculates the proper exposure, holds this data, and sets the exposureson one or more cameras appropriately at proper times in the photographicsequence. This exposure calculation and camera setting are preferablyaccomplished by modifying the camera employed in the photographicprocess, removing the light sensing element from its normal positionbehind the camera lens, mounting it in a moveable probe, and connectingit to electronic circuitry engineered to calculate a proper exposurefrom the probe outputs, to store such exposure data, and to transmitsuch exposure data to up to several cameras in delay sequence. Aschematic of the exposure-calculating and camera-controlling circuitryis shown in FIG. 1a.

After the proper exposure has been determined as discussed above, andthe camera has been set accordingly, the subject radiograph isphotographed on high resolution film as indicated in step 16, anddeveloped in a reversal process, the first developer solution of whichemploys a 3-pyrazolidone as the primary developing agent, as illustratedin step 18 of FIG. 1.

Full details of photographic chemistry of a negative developing processby which high resolution films may be developed for continuous tones inthe negative, and the specialized developing agents used to developthese films to give normal gradations of negative densities, are givenin U.S. Pat. No. 3,772,019 of Holden and Weichert, the full text ofwhich is hereby expressly incorporated herein by reference. It is to benoted, however, that U.S. Pat. No. 3,772,019 does not concern conditionsfor the production of negatives suitable for further processing in areversal process to yield positive images having gamma values in therange of 1.00 to 1.05, required in the present invention.

Prior to the Holden and Weichert patent, high resolution films had notbeen capable of being exposed at reasonable exposure indexes, and hadnot been developable to yield negatives having normal gradations of greytones. However, the developing process disclosed in U.S. Pat. No.3,772,019, employing a 3-pyrazolidone as the primary developing agent,as well as a secondary developing agent, overcomes both these problemsand produces negatives having extremely high resolution as well ascontinuous grey tones, suitable for producing high resolution continuoustone prints. In the present invention the conditions of this patent havebeen modified to produce high resolution intermediate negatives suitablefor further processing in a reversal process to yield high resolutionpositive images. In the reversal process the negatives are firstbleached, then reexposed and redeveloped to yield positives in themanner known to the art.

As shown in step 18 of FIG. 1, in the present invention the highresolution film is ultimately processed to a positive image having agamma value in the range of about 1.00 to about 1.05. To achieve finalhigh resolution positive images having these required contrast ratios,the exposed high resolution film is treated with a first developersolution containing as primary developing agent a 3-pyrazolidone,preferably phenidone, at a concentration of about 0.014 moles per literto about 0.025 moles per liter, and containing a secondary developingagent, preferably hydroquinone. The developer solution has a molar ratioof primary developing agent to secondary developing agent in the rangeof about 2.7:1 to about 6.8:1, corresponding to a weight ratio range ofabout 4:1 to about 10:1. The first developer solution most preferablycontains approximately 0.018 moles per liter of the primary developingagent, and approximately 0.006 moles per liter of the secondarydeveloping agent.

It is to be noted that the concentrations of primary and secondarydeveloping reagents shown above are substantially higher than thosetaught by the Holden and Weichert '019 patent, which concerned thepreparation of negatives for printing purposes. The maximum phenidoneconcentration called for in the '019 patent, is 0.0128 moles per liter,while the minimum phenidone concentration called for in the presentinvention is 0.014 moles per liter. The '019 patent teaches in column 9lines 32-43 that when one increases the primary developer to about 0.50g of phenidone per 240 ml of developer solution (0.0128 moles perliter), the concentration of hydroquinone secondary developer should bereduced to about 0.025 grams per 240 ml of developer solution (0.00094moles per liter). In the present application the lowest hydroquinoneconcentration in the first developer solution is 0.00205 moles per literdespite employment of phenidone concentrations above 0.0128 moles perliter.

The pH of the first developer solution is generally in the range 10.0 to10.5, and preferably about 10.3. The first developer solution isgenerally employed at a temperature in the range 68° to 95° F., for atime which depends on the developing agents, the concentrationsemployed, and the temperature selected, but which generally ranges fromabout 2 minutes to about 10 minutes. Following the first development,the resulting intermediate negative is successively bleached, cleared,reexposed, redeveloped with an active developer, fixed, washed, anddried, in a reversal developing process of the usual kind, as shown bythe box labeled 20 in FIG. 1.

An example of a film suitable for use in this invention is Jevaert CopexPan Rapid, which is a high resolution panchromatic black and white copyfilm which responds to wavelengths in the range of 400-700 nm. This filmis capable, in a good camera/lens system, using the developer describedabove, of providing 160 lines per mm resolution. It can typically beexposed at an ASA exposure index of 40 to 50 using the developing systemdiscussed above in which a 3-pyrazolidone is the primary developingagent. Other suitable high resolution films are KODAK AHU and FUJIMicrofilm HR, both of which are made with a clear base which isnecessary for production of a full-range reversal positive image.

For best photoreduction results, gamma values close to 1 are desired inthe final positive, as explained above. The ratio of primary developingagent and secondary developing agent in the first developer solution isadjusted for each type of film and for the selected developing agentsand conditions, to produce such final gamma values in the positive.Where the film is Copex Pan Rapid, a weight ratio of phenidone tohydroquinone of approximately 4:1 is preferably employed.

In an example of the photographic process of the invention, anindustrial radiograph is evenly illuminated from the rear andphotographed on 35 mm Jevaert Copex Pan Rapid high resolution film at anASA exposure index of 40-50, employing a camera which has opticsproducing no more than 0.1% total distortion. Additional radiographs aresimilarly photographed until the entire roll of copy film is exposed. Inthe dark the film is wound on a film-holding reel and placed in acovered developing tank. At this point, the lights are turned on, andall the chemical solutions for the film-developing process are preparedand equilibrated at the temperature desired for the development process,in this example, 68° F. The first developer solution is an aqueoussolution of phenidone and hydroquinone containing 0.0185 moles ofphenidone per liter and 0.0061 moles of hydroquinone per liter. Thefirst developer solution is poured into the developinq tank and the tankis recapped and struck sharply on the bench to dislodge air bubbles. Itis then agitated periodically in a manner known to the art for 3.5minutes while maintaining the development temperature at 68° F. Next,the first developer is poured out, the film in the tank is rinsedthoroughly with water, and a solution of bleaching agent is added. Thebleaching agent may be any conventionally known to the art, a particularone being a sulfuric acid solution of dichromate. After agitating thefilm in the bleaching agent for two minutes, the bleach is poured outand the top of the developing tank is removed. A clearing bath is nextadded to the developing tank and the film is agitated, to remove theyellow stain left by the bleaching agent. Any clearing bathconventionally known to the art may be employed, a 9% solution of sodiumsulfite being common. The clearing bath is removed and the film is nextunwound from the reel and reexposed in room light for approximately oneminute, then rewound on the film reel and replaced in the developingtank. Next, the second developer is added to the tank and the film isdeveloped for two minutes at the selected temperature of 68° F. Anyconventionally known active developer (as opposed to a compensatingdeveloper) may be employed in this step, D-19 and DEKTOL being suitableexamples. After the second development step is complete, the seconddeveloper is poured out and conventional fixing solution is added to thetank. After agitation for a few minutes, the fixer is poured out and thefilm is treated successively with a conventional hypo clearing agent,several water washes, and a wetting agent. Finally, the film is removedfrom the reel, shaken to remove as much liquid as possible, and hung ina clean environment to dry.

FIG. 2 shows a perspective view of a photographic copy stand useful inthe photoreduction process. It has a base 30 to which is attached acentral supporting pedestal 32. Two lightboxes 34 are mountedhorizontally on pedestal 32 at an angle of 90 degrees relative to eachother and supported by struts 36. These struts are shown more clearly inthe side view of the copy stand shown in FIG. 3. Each of the lightboxes34 provides illumination which is uniform over the entire surface of thelightbox, to within 10% of the illumination nominally provided by thelightboxes. Light sources having a color temperature in the range of3,800 to 7,000 degrees Kelvin are appropriately employed. Onecommercially available lightbox having the requisite uniformity ofillumination is the Aristo X-ray lightbox, available from Aristo GridLamp Products, Inc. In normal operation, the lightboxes are locked onfull output to provide maximum stability of operation, and for the caseof the Aristo X-ray lightbox, the color temperature of the resultingillumination is approximately 5,800° K.

Above lightboxes 34 is a unitary frame 38 which supports fourworkstations 40. For purposes of this discussion, the severalillustrated workstations 40 are designated 40a, 40b, 40c, and 40d, theletters indicating workstation positions about the copy stand. Thus forexample, 40b represents both a workstation 40 and a workstation positionb. Frame 38 is attached to pedestal 32 in a manner which permits it tobe rotated about the pedestal to selected positions, so that eachworkstation 40 may be positioned over each of the lightboxes 34 as wellas at positions not defined by the presence of lightboxes. The copystand is provided with a mechanism for holding the workstations in fixedpositions when frame 38 is not being rotated to locate the workstations.Any position-retaining mechanism known to the art may be employed, oneexample being a detent mechanism. Each workstation 40 includes arectangular clear piece of flat glass 42 at least as large as thelargest radiograph which is to be photographed. At the top of pedestal32 is a platform 44 which carries two camera-supporting arms 46, each ofwhich is shaped and disposed to hold a camera directly over respectiveones of the lightboxes 34. FIG. 4 shows the positioning of the twocameras over the workstations.

The copy stand is provided with a vibration reduction feature at each ofthe workstation positions at which photography is to be carried out.This comprises a ramp mechanism which operates to lift each workstationeasel out of frame 38 when it is properly positioned above a lightbox.Thus any vibration in the frame induced by operations being carried outat the set-ups and take-off workstations 40a and 40d are not transmittedto workstation positions 40b and 40c where photography is being carriedout.

In operation, a radiograph to be photographed is first placed on one ofthe workstations adjacent to a lightbox, for example, the workstationindicated in FIG. 2 as 40a. It is properly oriented on glass plate 42and held in place by means of an adjustable masking system such as ausual photographic enlarger easel, which prevents extraneous light fromoutside the radiograph from reaching the camera lens. Unitary frame 38is then rotated clockwise to place the radiograph to be photographedover lightbox 34 located in the adjacent workstation position 40b. Acorrect exposure is determined, and the camera above this workstation isappropriately set, in accordance with the photographic process describedabove. The camera located above the workstation position indicated as40c is set to the same exposure either manually or automatically viaappropriate electronics at an appropriate time. After the radiograph atworkstation position 40b has been photographed, unitary frame 38 isrotated clockwise 90 degrees to place the radiograph at workstationposition 40c where it is again photographed, by the second camera. Thetaking of identical photographs on each of two separate rolls of filmprovides duplicate original photoreductions, one of which is archivallystored while the other is kept available for ready reference. Frame 38is then rotated clockwise a further 90 degrees to place the radiographat workstation position 40d, where it is removed from the system.

During routine operation four radiographs are handled at any given timeby means of this photo stand. While the first radiograph is beingphotographed at workstation position 40b, a second radiograph is beingplaced on workstation position 40a and aligned. While the firstradiograph is being photographed at workstation position 40c, the secondradiograph is being photographed at workstation position 40b, and athird radiograph is being loaded and aligned at workstation position40a. Finally, when the first radiograph is being unloaded at workstationposition 40d, the second radiograph is being photographed at workstationposition 40c, the third radiograph is being photographed at workstationposition 40b, and a fourth radiograph is being loaded and aligned atworkstation position 40a. The cycle continues in this way until all theradiographs have been photographed on each of two separate rolls offilm. The films are identically developed and safely stored in twoseparate locations.

The radiographs are photographed at a 15-fold reduction in size. Anidentifying legend is preferably placed on each radiograph before it isphotographed. Normally this legend is placed along the top or bottomhalf-inch of the radiograph, in an area containing no informationrequired to be stored. Alternatively, an electronic counter with anilluminated display mounted at or near the plane of focus and at theedge of the light table is employed.

Workpieces to be X-rayed sometimes contain several areas of differentthicknesses within the larger area covered by the film being employed. Agiven film has a given latitude of exposure, outside of which the filmwill be over- or under-exposed. Thus, when a workpiece having varyingthickness is to be X-rayed, it is usually necessary to employ a sandwichof several films having different sensitivities or film speeds, toobtain properly exposed records of the several areas of interest. In thephotoreduction of the resulting radiographs, each of the films may bephotographed separately, but where each individual radiograph shows oremphasizes certain features of the X-rayed piece either not shown or notclearly shown in the other radiographs of the same piece, it isgenerally more efficient to photograph the several radiographssuperimposed one upon the other so that all of the features of the pieceare recorded on one film rather than several. This is easilyaccomplished on the photographic copy stand of the invention by aligningthe several radiographs carefully with respect to each other, placingmasks on all sides of the packet of radiographs exactly in the same waymasks are employed in photographing single radiographs on thisapparatus, then carefully determining a proper exposure andphotographing as discussed above. By thus photoreducing severalindividual radiographs to a single composite film, not only are storagecosts of the photographic records reduced, but later reexamination ofthe X-ray records of the parts under consideration is greatlyfacilitated since it is unnecessary to examine several individualradiographs.

For the benefits of the high resolution high accuracy photoreproductionprocess of the invention to be realized, a microfilm reader havingequally high resolution is required. Specifically, it is required thatan original radiograph not only be photoreduced with no more than 0.1%distortion, but that the resulting reduced negative be viewable at itsoriginal scale with no more than 0.1% distortion from the original.

Existing microfilm readers such as mirror and matte screen-based systemscommonly employed in libraries are totally inadequate for the task ofviewing a negative and permitting measurements of features on thenegative with the very high accuracy required for the present purpose.

The high resolution microfilm reader of the invention is shown in FIG. 5and possesses a supporting chassis 50 which has a generally uprightsection 50a and a base section 50b. The upright section 50a iscontiguous with one side of the base section 50b, the combination ofsections thus forming a generally L-shaped unit.

The base section has an upper surface 52 which includes a diffuser, suchas an opal diffuser, which is not shown in FIG. 5 but is located belowthe film holder 56 and movable platform 54 to be discussed below. Thisdiffuser is slightly larger than a 15×reduction of the largestradiograph to be accommodated, or about 26×30 mm. Supporting chassisbase section 50b includes means (not shown) for illuminating thediffuser from its underside and is typically a light source such as afluorescent tube. This will typically have a color temperature of about5,500° K. The light source may be located directly below the diffuser ormay be located elsewhere within the chassis, its light then beingdirected to the diffuser by means of appropriate reflectors.

Located on the top surface of chassis base section 50b is a movableplatform 54. This platform is mounted on chassis base section 50b sothat it rides slightly (about 1/4 inch) above base section surface 52.Platform 54 also has an opening located above the diffuser. This openingis not shown in FIG. 5 but is located below the film holder 56 to bediscussed below.

A film holder 56 is mounted on movable platform 54 above the opening inthe platform. Film holder 56 is preferably a pressure plate in the shapeof a frame having an opening the size of the film frame to be held. Inoperation, a film frame to be examined is placed between film holder 56and movable plate 54, then movable plate 54 is positionally adjusted inthe horizontal plane by movement of positioning control 58. It is lockedin the desired position by a positioning lock 60. The spacing betweenthe diffuser and movable plate 54 prevents any specks of foreignmaterial on the diffuser from being in focus when a film being examinedis in focus.

A focusing mount 62 is movably attached to the top of the chassisupright section 50a above chassis base section 50b. This attachment ispreferably by means of a rack and pinion mechanism, not shown in FIG. 5.Vertical adjustment is provided by turning focusing knob 64.

Mounted on the top of focusing- mount 62 is a binocular microscope head66 which includes eyepiece tubes 68. Attached to eyepiece tubes 68 areultrawide angle eyepieces 70, providing 15 power magnification.Eyepieces having other magnifications could in principle be employed.Mounted below focusing mount 62 is a beam splitter assembly housing 72which contains a beam splitter shown in FIG. 5a as 72d. The beamsplitter is preferably a beam splitter cube as shown in the figure. Thebottom of beam splitter assembly housing 72 is configured to connectwith a variable magnification objective lens 74, and the side of beamsplitter assembly housing 72 is similarly configured to accept a reticleassembly 76.

Objective lens 74 is a zoom lens providing a magnification range of fromsomewhat less than 1:1 to approximately 4.5:1. It is capable of viewingthe full frame of film being examined, in contrast to a microscopeobjective lens, which would only cover a small portion of the totalfield of a sample. The actual magnification provided by the lens isadjusted by magnification control 78.

Reticle assembly 76 is attached to the side of beam splitter assemblyhousing 72 and is shown schematically in FIG. 5a. It contains a reticle72a, a variable intensity light source 72b, and at least one opticalelement 72c to project an image of the reticle into the beam splitter72d. The reticle may be rotated to any desired orientation by means ofthe reticle position control 80.

Mounted along side of chassis base section 50b is a film transportingmechanism 82 which moves a strip of film under objective lens 74 forviewing. This film transport mechanism includes a film supply spool 84,a film take-up spool 86, an idler roller having alternating reflectiveand matte sections on its end, each of which corresponds to one frame,and which are sensed by an optical switch to provide an input to a filmcounter, the output of which is shown as 88 in FIG. 5, film tensioncontrol circuitry, and a motor/generator in each side of the filmtransport mechanism to drive each spindle and supply the film controlcircuitry with data necessary to keep proper film tension. Also includedis a control 90 for moving the film in forward and reverse directionsand controlling its speed.

A headrest 92 is optionally attached to the top of binocular microscopehead 66 to enhance the user's comfort.

In this system, each of the optical elements, that is, the binocularmicroscope head, the eyepiece tubes, the ultrawide angle eyepieces, thebeam splitter assembly, the objective lens, and the reticle assembly, isa high precision optical component, and the optical system taken as awhole has no more than 0.1% total distortion. 1 To further enhance theuser's comfort, the bottom of the unit is configured such that when theunit is set on a flat horizontal surface, it tips forward toward theuser. An adjustable elevator fool 92 is attached to the underside of thechassis base section 50b to permit raising the unit back to a verticalorientation in stages. The forward portion of the adjustable elevatorfoot 92 is located near the observer while the rear portion of theelevator foot is attached to the underside of the chassis base sectionnear the rear of the unit by means of a hinge. A support piece 94 ishinged to the front portion of the elevator foot 92 and is set to one ofa number of detent positions on the underside of chassis base section50b in order to fix a desired tilt angle for the microscope reader.

A number of the parts of the high resolution reader are commerciallyavailable. These parts and their respective suppliers are listed below.Focusing mount 62 is a Nikon focusing mount No. 76012. Binocularmicroscope head 66 is a Nikon Binocular Body Tube B, No. 79004. Betweenthe focusing mount and the microscope head is Binocular Adaptor byAmarel Precision Instruments Company, No. 284006. The eyepieces 70 aremade by Bausch and Lomb, No. 31-15-74-02. Beam splitter assembly 72 andreticle assembly 76 are a Reticle Projector Assembly produced by AmarelPrecision Instruments. Company, No. 287004. The lamp for this unit isNo. 296004 of Amarel Precision Instruments Company, which also suppliesa dimmer control, No. 276007. Objective lens 74 is a VariableMagnification Objective by Amarel Precision Instrument Company, No.29901. The film transporting mechanism 82 and associated apparatus is aMotorized Roll Film Attachment Model PP by the Micro Design division ofBell & Howell. The reflector, mirrors, and diffuser of the illuminationsystem for the reader are by American Photo Systems, Inc., and theillumination system includes type 7452 lamps for a Durst 601 enlarger,and an Aristo Attenuator, available from Aristo Grid Lamp Products, Inc.

Other embodiments of the invention will be apparent to those skilled inthe art from a consideration of this specification or practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with the true scope and spiritof the invention being indicated by the following claims.

What is claimed is:
 1. A high resolution microfilm reader including an optical system having no more than 0.1% total distortion, comprising:a supporting chassis; a focusing mount adjustably attached to said chassis; a binocular microscope head attached to said focusing mount and having first and second eye piece tubes and corresponding first and second ultrawide-angle eye pieces; a beam splitter assembly attached to said focusing mount and having a beam splitter housing; a variable magnification objective lens, attached to said beam splitter housing, for providing said beam splitter assembly with an image of a microfilm being viewed; a reticle assembly, attached to said beam splitter housing and having a rotatable calibrated reticle for measuring features of said microfilm image being viewed, and means including at least one optical component for projecting an image of said reticle into said beam splitter assembly; and said beam splitter assembly further including a beam splitter, for receiving said image of a microfilm being viewed and said reticle image, and for simultaneously providing both of said first and second eye pieces with said image of a microfilm being viewed and said reticle image.
 2. The reader of claim 1 wherein said chassis further includes a base section having an upper surface which includes a diffuser.
 3. The reader of claim 2 wherein said chassis base section includes means for illuminating said diffuser from the underside.
 4. The reader of claim 2 wherein said chassis base section further comprises a movable platform slightly spaced above said base section upper surface, said platform having an opening above said diffuser.
 5. The reader of claim 4 wherein said movable platform further comprises means for holding a film across said opening in said platform.
 6. The reader of claim 5 wherein said means for holding comprises a pressure plate having an opening therethrough at least the size of said film.
 7. The reader of claim 2 further comprising means for transporting strip film between said objective lens and said upper surface of said chassis base section, said transporting means including means for maintaining a desired tension on said strip film, means for counting frames, and means for moving said strip film in forward and reverse directions at a desired speed.
 8. The reader of claim 1 wherein said ultrawide-angle eyepieces are 15×magnification.
 9. The reader of claim 1 wherein said objective lens is a zoom lens providing a magnification range of from somewhat less than 1:1 to approximately 4.5:1.
 10. The reader of claim 1 wherein said reticle assembly projecting means further comprises an adjustable light source.
 11. The reader of claim 1 further comprising means for tilting said reader from a generally upright orientation toward an observer to one of a plurality of orientations at angles from said upright orientation.
 12. A high resolution microfilm reader, comprising:a supporting chassis having a generally upright section and a base section, said upright section having a top and being contiguous with one side of said base section, said base section having an upper and a lower surface; a focusing mount having top and bottom sides, adjustably attached to the top of said chassis upright section above said chassis base section such that the vertical position of said mount relative to said chassis may be adjusted; a binocular microscope head, attached to the top side of said focusing mount, said binocular head further comprising eyepiece tubes and ultrawide angle eyepieces; a beam splitter assembly, attached to the bottom side of said focusing mount, said beam splitter assembly further comprising a beam splitter cube and a housing for holding said beam splitter cube, said housing having a bottom and a side configured respectively to connect with first and second image forming systems, for simultaneously providing first and second images to each eyepiece of said binocular microscope head; a variable magnification objective lens, attached to the bottom of said beam splitter housing, said objective lens constituting said first image forming system for providing said first image; a reticle assembly, attached to the side of said beam splitter housing, said reticle assembly constituting said second image forming system for providing said second image, and further comprising a reticle, a light source, and at least one optical component capable of projecting an image of said reticle into said beam splitter cube; and the optical system of said microfilm reader taken as a whole having no more than 0.1% total distortion. 